In a processing apparatus of a substrate such as a semiconductor wafer, an electrostatic chuck is widely used to support and hold the substrate. The electrostatic chuck is formed of a dielectric on a surface of a mounting table of the substrate and a metal electrode plate is buried right under the dielectric. A high voltage DC power is applied to the electrode plate to adsorptively hold the substrate by a Coulomb force or a Johnson-Rahbek force.
Further, in a plasma processing apparatus, since a wafer serving as a substrate to be processed receives heat from above, the mounting table of the substrate is formed of a material such as metal having a high thermal conductivity and a coolant path is provided inside the mounting table to cool the mounting table. Further, a heat transfer gas such as He gas is introduced into a gap between the mounting table and a backside of the wafer to facilitate cooling of the wafer.
A power feed line is connected to the electrode plate of the electrostatic chuck to supply a voltage applied from a power supply to the electrode plate. The power feed line may be provided at a central portion of the mounting table as disclosed in, e.g., Japanese Patent Laid-open Publication No. 2000-317761, and may be provided at a peripheral portion of the mounting table as disclosed in, e.g., Japanese Patent Laid-open Publication No. 2001-274228.
Since a voltage applied to the electrode plate of the electrostatic chuck is a high voltage, the power feed line needs to be surrounded by an insulating material. Generally, since the insulating material has a low thermal conductivity, the insulating material surrounding the power feed line is different from a portion made of a material having a high thermal conductivity in the heat transfer amount from the substrate to the mounting table. That is, in the vicinity of the power feed line, an amount of heat transferred to the coolant is small and a surface temperature of the substrate increases. Accordingly, since an amount of heat dissipated from the substrate to the mounting table becomes small in the vicinity of the power feed line, the substrate temperature in this portion becomes higher than that in the other portion. Therefore, for example, in a plasma etching process, an undesirable difference in characteristics of the etching process may occur between a portion in the vicinity of the power feed line and the other portion.